Device for detecting near end state of a roll of paper

Abstract: A device has a pivoted lever (24) for detecting a near end state of a roll of paper, and the lever (24) is held at a first position by the weight of a roll of paper, but is resiliently biased toward a second position by a spring (32). When the roll of paper does not have a core, and when the weight thereof falls to a predetermined value, the lever is moved from the first position to the second position due to a resilient force of the spring (32). When the roll of paper has a core, and when a diameter thereof is reduced to a predetermined value, the lever (24) receives the roll of paper in a recess (34) formed therein, and is moved from the first position to the second position due to a resilient force of the spring (32). When the lever is moved to the second position, this is detected by a suitable detecting element (40). Thus, the detector can detect the near end state of the roll of paper without regard to whether the roll of paper has a core or not.

Description: The present invention relates to a device for detecting the near end state of a rotatably-held roll of paper after paper has been drawn from the roll. More particularly, the device can be built into a printer, facsimile, or other recording apparatus which uses a roll of paper as a recording medium. The term "near end state" is used herein to mean the state when there is only a small amount of the roll of paper remaining. A printer mounted in a terminal of a POS (point of sale) system or register usually uses a roll of paper as a recording paper therefor. Frequently, the roll of paper is held in the system at a position where it cannot be observed. As a result, the near end state of the roll of paper cannot be visually determined by the user. Accordingly, if the time for reloading a new roll of paper in the printer is missed and the roll already located therein runs out, data to be recorded can be lost. To avoid this undesirable situation, a detector for detecting the near end state of the roll of paper is built into the printer, and functions to notify the user when the time has come to place a new roll of paper in the printer. Known near end state detectors can be considered to be one of two types; one is a type which detects the diameter of the roll of paper, while the other is a type which detects the weight of the roll of paper. The former type is used mainly when the roll of paper has a core, and indicates when the diameter of the roll has been reduced to a predetermined value due to the use of paper therefrom. The latter type is mostly used when the roll of paper has no core, and indicates when the weight of the paper falls to a predetermined value due to the use of the paper from the roll. A printer having either of the two known types of detector suffers from the problem that the type of roll of paper which can be used is limited by the type of the near end detector built into the printer, even though any roll of paper, having a core or not, can be used for recording. In particular, for example, when a coreless roll of paper is used in a printer having a built-in near end detector of the type which detects the diameter of the roll of paper, accurate detection of the near end state of the roll of paper is not possible and the time for loading the new roll of paper is therefore often missed. This is because, when the amount of paper remaining in the roll becomes small, it loosens and the diameter of the roll appears to increase, so it is not possible to detect accurately the diameter of the roll. On the other hand, even when a roll of paper with a core is used in a printer having a built-in near end detector of the type detecting the weight of the roll of paper, it is not possible to detect the near end state of the roll of paper and therefore the time for loading a new roll of paper is often missed. This is because it is not possible to detect accurately the weight of the roll of paper itself due to the weight of the core of the roll. In the prior art, JP-A-61-116573 discloses a detector having all of the features of the preamble of claim 1. Therefore, an object of the present invention is to provide a detector for detecting the near end state of a rotatably-held roll of paper which can detect the near end state whether or not the roll of paper has a core. In accordance with the present invention, there is provided a device for detecting the near end state of a roll of paper, comprising: holding means for rotatably receiving a roll of paper such that paper can be drawn from the roll; movable means arranged so as to be movable between a first position and a second position which is indicative of the near end state of the roll of paper, resilient means for resiliently biasing said movable means towards said second position; and detecting means for detecting when said movable means is in said second position, characterised in that said movable means comprises a lever element having a roll-receiving recess formed therein, which recess is defined between a first step portion and a second step portion, said first step portion being movable towards and away from the pivot point of said lever element, wherein, in use, a roll of paper contacts said movable means such that the weight of the roll of paper acts against said resilient means so that said movable means is retained in said first position until, owing to paper being drawn from the roll, either (a) the weight of the roll decreases to the extent that the resilient means is able to move the movable means into said second position, or (b) the diameter of the roll decreases to the extent that the roll is received in said roll-receiving recess thereby causing the movable means to move to said second position, the position of said first step portion relative to the pivot point of the lever element determining the diameter of the roll of paper at which the roll of paper is received in said roll-receiving recess. In one embodiment, the device of the invention further comprises an alarm means for warning that the remaining amount of the roll of paper has reached the near end state when the movement of the movable means from the first position to the second position is detected by the detecting means. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:- Figure 1 is a schematic perspective view showing part of a printer mounted on a terminal of a POS system in which is incorporated a device for detecting the near end state of a roll of paper in accordance with the present invention; Figure 2 is a perspective view showing in detail a lever element constituting a part of a device in accordance with the present invention; Figure 3 is a partially cutaway enlarged perspective view of the printer shown in Fig. 1, showing a coreless roll of paper before the near end state thereof; Figure 4 is a view similar to that of Fig. 3, showing a coreless roll of paper in the near end state; Figure 5 is a view similar to that of Fig. 4, which shows a roll of paper, with a core, in the near end state. Figure 6 is a side view of Fig. 5 which shows an example of an adjustment of the lever element; Figure 7 is a block diagram of the controller of a device in accordance with the present invention; and Figure 8 is a flow chart for explaining the operation of the controller of Fig. 7. Figure 1 schematically shows a printer mounted, for example, in a terminal of a POS system. This printer is provided with a frame 10, a platen 12 disposed above the frame 10, and a thermal head 14 disposed close to and facing the platen 12. The platen 12 and the thermal head 14 are both supported by the frame 10 through a suitable support structure (not shown). The frame 10 includes a standing portion 10a exhibiting a box-like shape and a protruding portion 10b which extends from the bottom of the standing portion 10a in the horizontal direction. A roll of paper holding space is formed between the two portions 10a and 10b. A pair of support rollers 16 is rotatably disposed in each of the standing portion 10a and the protruding portion 10b. When a roll of paper RP, shown by the chain-dot line, is loaded in the roll of paper holding space, the roll of paper RP is placed on the two pairs of support rollers 16, whereby the roll of paper RP is held in a rotatable manner. Further, six rib elements 18 are provided at equal intervals between the two pairs of support rollers 16, and extend on the protruding portion 10b in a direction perpendicular to the centre axis of the roll of paper RP and rise vertically along the wall surface of the standing portion 10a. The two outermost rib elements are formed integrally as part of the two side walls of the frame 10. The paper P drawn out from the roll of paper RP is guided through two guide rollers 20 and 22, and is fed to a space between the platen 12 and the thermal head 14, whereby a recording is made on the paper P by the thermal head 14 during the passage of the paper P into that space. The two guide rollers 20 and 22 are supported by the frame 10 through a suitable support structure (not shown). During the recording operation by the thermal head 14, the paper P is drawn out from the roll of paper RP and, accordingly, the diameter of the roll of paper RP gradually becomes smaller and the weight of the roll of paper decreases. When the roll of paper RP is first loaded, that is, when the diameter of the roll of paper RP is large and its weight is relatively heavy, the roll of paper RP is held in a rotatable manner by the two pairs of support rollers 16. On the other hand, when the diameter of the roll of paper RP becomes small and its weight is relatively less, the roll of paper RP is made to rotate on the rib elements 18. However, since the contact area between the rib elements 18 and the roll of paper RP is small, the frictional resistance at the time of rotation of the roll of paper RP is also small. Referring to Fig. 2, a detector for detecting the near end state of the roll of paper according to the present invention includes a lever element 24 which acts as the element to be detected. The lever element 24 is built into the protruding portion 10b of the frame 10, as shown in Fig. 1, and is arranged between the two middle rib elements 18. As shown in Fig. 2, one end of the lever element 24 is pivoted between a pair of mounting members 26 extending from the end wall of the protruding portion 10b, while a part 28 to be detected projects from the other end. As shown in Fig. 1, the part 28 to be detected is inserted through an opening 30 formed at the bottom of the side wall of the standing portion 10a of frame 10. A coil spring 32 acts against the pivot end of the lever element 24, so that the lever element 24 is elastically biased at all times in the direction shown by the arrow A (Fig. 2). The lever element 24 comprises two portions, that is, a first portion 24a with the pivot end and a second portion 24b with the part 28 to be detected. A recess 34 is formed in the second portion 24b. The size of the recess 34 is adjustable due to the movable connection of a U-shaped slider with the first portion 24a. More specifically, two plate spring-like connecting pieces 36 project from the U-shaped slider, and are slidably received and connected in a groove portion 38 formed in the first portion 24a. One of the plate spring-like connecting pieces 36 has a projection 36' integrally formed at a free end thereof, and one of the side wall surfaces of the groove portion 38 has several depressions 38' formed therein. As shown in Fig. 2, the projection 36' can be elastically engaged with one of the depressions 38'. In short, by selecting the engagement position of the projection 36', the size of the recess 34 of the second portion 24b is adjustable. The significance of the adjustment of the size of the recess 34 will be explained in detail later. The near end state detector further comprises a gate-like element 40 as an optical detection means, which is provided inside the standing portion 10a of the frame 10, as shown in Fig. 1. A light-receiving element is built into one leg portion of the gate-like element 40, while a light-emitting element, such as a semiconductor laser, is built into the other leg portion. A light beam is emitted from the light-emitting element towards the light-receiving element. In Fig. 3 to Fig. 5, the light beam is shown by the reference characters LB. Part 28 of the lever element 24 is received in the gate-like element 40, and is used to detect the near end state of the roll of paper RP in the manner described below. When the roll of paper RP is loaded in the roll of paper holding space of the frame 10, as shown in Fig. 1, the weight of the roll of paper causes the lever element 24 to be retained in a first position, that is, a pushed-in position, against the elastic force of the coil spring element 32. At that time, the part 28 of the lever element 24 is in a lower position in the gate-like element 40, so it will not break the light beam traversing the inside of the gate-like element 40. The roll of paper RP shown in Fig. 1 does not have a core, but the above is true for a roll of paper with a core. Figure 3 shows when a considerable amount of paper P has been drawn out from the coreless roll of paper RP and the roll is approaching the near end state. The lever element 24 is still retained at the pushed-in first position by the weight of the roll of paper RP, so that the light beam LB is not broken by the part 28 of the lever element 24. Figure 4 shows the state where the roll of paper RP has reached the near end state. At this time, coil spring 32 is able to overcome the weight of the roll of paper RP. Accordingly, the lever element 24 is moved from the first pushed-in position to a second position, where the part 28 of the lever element 24 abuts against the bottom surface of the top portion of the gate-like element 40. As a result, the light beam traversing the inside of the gate-like element 40 is broken and a detection signal is generated by the light-receiving element built into one of the leg portions of the gate-like element 40. Thus, when the roll of paper RP does not have a core, the near end state thereof is detected by detecting the reduction in weight of the roll. Figure 5 shows the state where a roll of paper RP with a core C has reached the near end state. The weight of the core C may be such that it by itself can retain the lever element 24 in the first, pushed-in position. However, when the roll of paper RP with a core reaches the near end state, the diameter is reduced to such an extent that it can be received in the recess 34 of the lever element 24. At this time, the pressing force from the roll of paper RP with the core on the lever element 24 is released, so that the lever element 24 is moved from the first position to the second position (in the same way in the case of a coreless roll of paper RP) by the elastic force of the coil spring element 32. As a result, a detection signal is generated by the light-receiving element built into one of the leg portions of the gate-like element 40. There are various rolls of paper having cores with different diameters on the market. To detect the near end states of these various rolls, it is necessary to adjust the size of the recess 34 of the lever element 24. As mentioned above, by making the U-shaped slider move with respect to the second portion 24b of the lever element 24, it is possible to adjust the size of the recess 34, so it is possible to detect the near end state of rolls of paper having cores of different diameters. Of course, the larger the core diameter, the closer the U-shaped slider is set to the pivot end of the lever element 24, while the smaller the core diameter, the closer the U-shaped slider is set to the detection end of the lever element 24. For example, in the case where the core diameter of the roll of paper is 22.2 mm, and where the near end state (i.e. the remaining paper length) of the roll of paper is 1.5 m, it is sufficient to detect when the total diameter of the roll of paper decreases to 25.5 mm. In this case, as shown in Fig. 6, the step portion of the U-shaped slider that defines the end of the recess 34 at the pivot end of the lever element 24 is positioned to be 41.4 mm from the pivot centre. With this arrangement, if the total diameter of the roll of paper falls to 25.5 mm, the lever element 24 swivels 2.85 degrees from the first, pushed-in position due to the elastic force of the coil spring 32. At this time, the part 28 of the lever element 24 rises about 2 mm in the vertical direction and cuts off the light beam LB. When a detection signal is output from the light-receiving element, a suitable alarm means can be operated to warn the user that the roll of paper has reached the near end state. By way of example, Figure 7 shows a block diagram of the control for this alarm system. In this drawing, reference numeral 42 shows a control circuit of a terminal of a POS system, by which control circuit 42 the near end detector is controlled. The control circuit 42 comprises a microcomputer which includes a central processing unit (CPU) 42a, a read only memory (ROM) 42b for storing various operational programs, constants, etc., a random access memory (RAM) 42c for temporarily storing data etc., and an input/output interface (I/O) 42d. In Fig. 7, the light-receiving element built into one leg portion of the gate-like element 40 is indicated by reference numeral 44 and the light-emitting element built into the other leg portion of the gate-like element 40 is indicated by reference numeral 46. The light-emitting element 46 is connected through a power circuit 48 to input/output interface 42d. When an ON signal is output from the control circuit 42 to the power circuit 48, the light-emitting element 46 is electrically energized and a light beam LB is emitted toward the light-receiving element 44. While the light beam LB is incident on the light-receiving element 44, the detection signal from the light-receiving element 44 is at the low level "L", but once the incidence of the light beam LB on the light-receiving element 44 is cut off, the detection signal from the light-receiving element 44 rises from the low level "L" to the high level "H". Further, in Fig. 7, reference numeral 50 indicates an alarm lamp which is provided at a suitable location on the housing (not shown) of the printer shown in Fig. 1. This alarm lamp 50 is connected through the power circuit 52 to input/output interface 42d. When an ON signal is output from the control circuit 42 to the power circuit 52, the alarm lamp 50 is electrically energized and is lit. Reference numeral 54 shows a power switch of a terminal of a POS system. Next, an explanation will be made of the operation of the near end detector referring to the near end detection routine shown in Fig. 8. The near end detection routine of Fig. 8 is an interruption routine. When the power switch 54 shown in Fig. 7 is turned ON, this routine is repeatedly executed at suitable time intervals, for example, every second. At step 701, an ON signal is output from the control circuit 42 to the power circuit 48 of the light emitting element 46, whereby a light beam LB is emitted from the light-emitting element 46 toward the light-receiving element 44. Then, at step 702, the signal from the light-receiving element 44 is monitored. This monitoring may be performed at one second intervals. As mentioned above, the signal from the light-receiving element 44 is held at the low level "L" while the light beam LB is incident on the light-receiving element 44. However, once the emission of the light beam LB to the light-receiving element 44 is cut off, the signal rises from the low level "L" to the high level "H". The disappearance of the light beam LB at the light-receiving element 44 is caused by the part 28 of the lever element 24. This signifies that the roll of paper RP is at the near end state. When the detection signal from the light-receiving element 44 is held at the low level "L", the routine proceeds from step 702 to step 703 and an OFF signal is output from the control circuit 42 to the power circuit 52 of the alarm lamp 50, so the alarm lamp 50 will not light up. On the other hand, when the detection signal from the light-receiving element 44 rises to the high level "H", the routine proceeds from step 702 to step 704. At this time, an ON signal is output from the light-receiving element 44 to the power circuit 52 of the alarm lamp 50, whereby the alarm lamp 50 is lit and the user is warned that the roll of paper RP is near its end. This enables the user to insert a new roll of paper into the printer at a suitable time. In the above-described embodiment, the near end detector is used for a printer of a terminal of a POS system, but needless to say it may also be used for other recording apparatuses, such as a facsimile. Further, in the above-described embodiment, an optical detecting means was used for detecting the part 28 of the lever element 24, but use may also be made of other detecting means, for example, a microswitch. As is clear from the above description, with the near end detector according to the present invention, it is possible to detect the near end state of a paper roll regardless of whether the roll of paper has a core or not. Thus, unlike the prior art, there is no limitation on the type of roll of paper which may be used.

Claims: A device for detecting the near end state of a roll of paper (RP), comprising: holding means (16,18) for rotatably receiving a roll of paper (RP) such that paper can be drawn from the roll; movable means (24,24a,24b) arranged so as to be movable between a first position and a second position which is indicative of the near end state of the roll of paper, resilient means (32) for resiliently biasing said movable means (24,24a,24b) towards said second position; and detecting means (40) for detecting when said movable means (24,24a,24b) is in said second position, characterised in that said movable means (24,24a,24b) comprises a lever element (24) having a roll-receiving recess (34) formed therein, which recess (34) is defined between a first step portion and a second step portion, said first step portion being movable towards and away from the pivot point of said lever element (24), wherein, in use, a roll of paper (RP) contacts said movable means (24, 24a, 24b) such that the weight of the roll of paper (RP) acts against said resilient means (32) so that said movable means (24,24a,24b) is retained in said first position until, owing to paper being drawn from the roll (RP), either (a) the weight of the roll (RP) decreases to the extent that the resilient means (32) is able to move the movable means (24,24a,24b) into said second position, or (b) the diameter of the roll (RP) decreases to the extent that the roll (RP) is received in said roll-receiving recess (34) thereby causing the movable means (24,24a,24b) to move to said second position, the position of said first step portion relative to the pivot point of the lever element (24) determining the diameter of the roll of paper (RP) at which the roll of paper (RP) is received in said roll-receiving recess (34). A device as claimed in claim 1, further comprising an alarm means for warning that the remaining amount of the roll of paper (RP) has reached the near end state when the movement of said movable means (24,24a,24b) from the first position to the second position is detected by said detecting means (40).

Inventors: SKELLY EAMON, YOSHIDA KOHICHI, SKELLY, EAMON, YOSHIDA, KOHICHI, SKELLY, EAMON, C/O FUJITSU ISOTEC LIMITED, YOSHIDA, KOHICHI, C/O FUJITSU ISOTEC LIMITED
Applicants: FUJITSU ISOTEC LTD, FUJITSU ISOTEC LIMITED
Application year: 1994
Main classification: B65H26
IPC codes: B65H16, B41J15, B65H43, B65H26, B41J29